icons: swap the 4 kit-available icons in footer-home to the sprite (proof)

Home/Archive/Chat/Contact (house/box-archive/comment/envelope) now render from
icons.svg via <use href=#dw-…>; the other 20 footer FA icons stay until the kit
is topped up. Proves the sprite pipeline end-to-end on a live surface.

parts/footer-home.html

@@ -5,18 +5,18 @@
 			<div class="col-md-4">
 				<ul style="float:left;margin-right:10px;">
 					<li><a href="/about"><span class="fa fa-file-text-o fa-fw"></span> About</a></li>
-					<li><a href="/desk/archive" title="Archive"><span class="fa fa-archive fa-fw"></span> Archive</a></li>
+					<li><a href="/desk/archive" title="Archive"><svg class="dw-icon" aria-hidden="true" focusable="false"><use href="#dw-box-archive"></use></svg> Archive</a></li>
 					<li><a href="/studio/music/"><span class="fa fa-microphone fa-fw"></span> Audio</a></li>
-					<li><a href="https://davidwindham.com/rtc"><span class="fa fa-comment fa-fw"></span> Chat</a></li>
+					<li><a href="https://davidwindham.com/rtc"><svg class="dw-icon" aria-hidden="true" focusable="false"><use href="#dw-comment"></use></svg> Chat</a></li>
 					<li><a href="http://chess.davidwindham.com"><span class="chess-html">&#9814;</span> Chess</a></li>
 					<li><a href="http://code.davidawindham.com"><span class="fa fa-code fa-fw"></span> Code</a></li>
-					<li><a href="/contact"><span class="fa fa-envelope-o fa-fw"></span> Contact</a></li>
+					<li><a href="/contact"><svg class="dw-icon" aria-hidden="true" focusable="false"><use href="#dw-envelope"></use></svg> Contact</a></li>
 				</ul>
 				<ul style="float:left;margin-right:10px;">
 					<li><a href="/desk"><span class="fa fa-pencil-square-o fa-fw"></span> Desk</a></li>
 					<li><a href="/mail/" title="Newsletter"><span class="fa fa-paper-plane-o fa-fw"></span> Email</a></li>
 					<li><a href="/contact/guests" title="Guestbook"><span class="fa fa-pencil-square fa-fw"></span> Guests</a></li>
-					<li><a href="/"><span class="fa fa-home fa-fw"></span> Home</a></li>
+					<li><a href="/"><svg class="dw-icon" aria-hidden="true" focusable="false"><use href="#dw-house"></use></svg> Home</a></li>
 					<li><a href="/studio/art/" title="Art"><span class="fa fa-paint-brush fa-fw"></span> Paint</a></li>
 					<li><a href="/pay"><span class="fa fa-credit-card fa-fw"></span> Pay</a></li>
 				</ul>